When human joints, such as the knee, become diseased or otherwise are incapable of functioning, surgical intervention is possible. Surgeons expose the junction between the tibia and the femur, temporarily disconnect the patella, resect away parts of the femur or tibia or both, and replace the ends of the femur and tibia with artificial prostheses. Orthopedic implants for the human knee generally have a femoral and tibial component. The tibial component is usually placed on the resected proximal surface of the tibia and frequently has a metal base plate with a shaft extending into the medullar canal. The base plate usually carries an ultra high molecular weight polyethylene (UHMWPE) articulating surface. The articulating surface has medial and lateral condyle compartments, approximating the medial and lateral condyle compartments of a natural tibia in form and function. A femoral component is implanted on a resected distal end of the femur and presents artificial condyles, similar in form and function to the natural condyles of the femur which have been cut away, which articulate with the condyle compartments of the tibial component. A femoral component generally comprises the condyle articulating surfaces and fixation means, which may include an elongated stem extending into the medullar canal of the patient. Such prostheses are well known and examples can be found in U.S. Pat. Nos. 4,963,152; 5,062,852; and 5,071,438.
For patients who require an artificial knee prothesis, degeneration of the bone at either the tibia or femur or both may be occurring. Moreover, this degeneration may be proceeding unevenly with respect to the two condyles, or the two condyle compartments. A side effect of this degeneration is that the anatomic alignment of the femur to the tibia may become disjointed causing an imbalance to the collateral ligaments. It is known that some patients require a re-operation and the installation which is called a "revision" knee prosthesis. The revision knee prosthesis is generally more massive than a so-called "primary" knee prosthesis. The revision femoral knee condylar parts may be thicker and more robust and the medullar shaft may be substantially longer. Moreover, in many cases, degeneration of one condyle may be substantially more advanced than the other.
Whether natural or prosthetic, the knee joint is supported by the patella and by ligaments, including the medial and lateral collateral ligaments on either side of the knee, and the cruciate ligaments behind the knee. If present, these ligaments, particularly the collateral ligaments, must be under proper tension, and balance, both when the knee is in extension and when it is in flexion, in order to maintain correct anatomic alignment. It is important, therefore, for a surgeon performing knee replacement surgery to be able to size the prosthesis and place resection cuts appropriately so that the reassembled knee will cooperate with the ligaments to form a stable joint. This is particularly problematic in the case of revision surgeries, where substantial changes in the bone structure, and also changes in the balance of the medial and lateral collateral ligaments may be expected.
In the past, surgeons have placed the exposed knee joint under tension both in extension and flexion either manually, or by use of instruments. There remains a need, however, for instrumentation which can enable the surgeon to spread the joint between the distal femur and the proximal tibia, placing the collateral ligaments in tension, both when the knee is in flexion and in extension in an effort to establish the balance of these ligaments with respect to the correct, or corrected, anatomic alignment of the knee joint. Moreover, such apparatus is needed which would operate on both condyles simultaneously to place the medial and lateral collateral ligaments in tension.